Try this and see if it works.
Try following these steps to change the device back to English:
1. Connect to the web configuration utility by entering the TeraStation's IP address in a web browser.
2. In the column of blue items on the left hand side, select the second link.
3. Under the first header are two text fields; enter or modify the text in the second.
4. Under the third header, the first entry is a radio selection with two options; select the one on the right.
5. Under the fourth header (with two menu/pulldown boxes beneath it), set both menu boxes to the second entry in the list (the second menu box should say cp437).
6. Click the button, and close and reopen the browser.
If this does not fix the problem, try to reflash the firmware. If possible, it would be wise to backup any important data in case the firmware update fails due to a power outage or other anomaly. If you have the latest version already, you will need to force the firmware update. To do this, after unzipping the files, create a shortcut to the .exe file. Then, go to the properties of the shortcut and add a space and /force to the very end of the target.
EX: "C:\Buffalo\Firmware\TeraStation\112-103\HD-HTGL FWUpdate.exe" /force
Then run the shortcut to flash the firmware. After flashing the firmware, you'll need to restore the device to factory defaults using the web interface, by following the following steps.
1. Connect to the web configuration utility as before.
2. In the column of blue items on the left hand side, select the second from bottom link (icon shows wrench and screwdriver).
3. Under that link, five subcatagory links should show up. Select the fifth link.
4. Under the second header there is a single buttom; click it.
5. Click the yes button to start the configuration restore.
6. This will reset all settings, including ip address and hostname, so you'll need to set the device up as if it was new.
7. Go through the above steps again to change the language.